JP2000284836A - Regulated power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a regulated power supply circuit not to be affected by electromagnetic wave noise. SOLUTION: Outputted voltage is made to be constant by outputting current to a transistor 12 according to output of an amplifier 11 by the regulated power supply circuit 10. A feedback line 14 of the amplifier 11 is provided with a noise removal filter C1 to remove high frequency noise. An output terminal of the amplifier 11 is similarly provided with a noise removal file C2 to remove high frequency noise as well. The high frequency noise entering from each terminal is removed by the noise removal filters C1, C2. Thus, amplitude of the high frequency noise of a transistor in the amplifier 11 and a base terminal of the output transistor 12 is suppressed and lowering of the outputted voltage due to a current action of the transistors is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a stabilized power supply circuit for supplying a constant voltage. In particular, by providing a filter for removing high-frequency noise in the feedback circuit of the amplifier and not feeding back the effect of high-frequency noise,
The present invention relates to a stabilized power supply circuit that maintains a constant voltage. The present invention
The present invention can be applied to an electronic control device used in an environment with much electromagnetic noise, for example, a vehicle.

[0002]

2. Description of the Related Art Conventionally, there is a stabilized power supply circuit called a regulator IC. In this method, an unstable DC voltage is input and a stable DC voltage is output. FIG. 7 shows the configuration. The stabilized power supply circuit 10 mainly includes an amplifier 11, a transistor 12 for supplying a current according to the output thereof, a feedback circuit 13 for monitoring the output of the transistor 12 and feeding it back to the amplifier 11, and a reference voltage for supplying a reference voltage to the amplifier 11. It comprises a generating circuit 15. In this configuration, the amplifier 11 has the monitor resistor R
1 and R2, the monitor voltage is monitored, and the current of the transistor 12 is controlled so that the monitor voltage becomes equal to the reference voltage. The feedback circuit 1
3 includes a feedback line 14 and a monitor resistor R
1, R2.

For example, when the output voltage slightly increases due to a load change, the amplifier 11 detects the output voltage by using a voltage generated at a monitor resistor and compares the detected voltage with a reference voltage. Then, a voltage corresponding to the difference is output to the transistor 12, and the emitter current is reduced. Due to this decrease in the emitter current, the monitor voltage and the reference voltage become equal again. As a result, the output voltage is always kept constant. The output voltage V _OUT1 is determined by the following equation if the ON resistance of the transistor 12 is ignored.

V _OUT1 = V _R · A / (1 + γA) ≒ V _R / γ (1) where V _R is the reference voltage, A is the gain of the amplifier 11, and γ
Is a feedback amount determined by the divided monitor resistors. γ is
It can be expressed by the following equation.

Γ = R2 / (R1 + R2) (2)

[0004] Generally, in this type of stabilized power supply circuit, a noise removing filter for removing high-frequency noise is connected between an input terminal and a ground terminal and between an output terminal and a ground terminal. This is to prevent a malfunction such as an output voltage fluctuating due to high-frequency noise entering from an input or output terminal. For example, capacitors C11 and C22 are connected to the input terminal and the output terminal, and high-frequency noise is bypassed to the ground.

[0005]

However, the external mounting of the noise elimination filter increases the size of the stabilized power supply circuit. This does not meet the recent demand for space saving and miniaturization. In addition, the external mounting step has a disadvantage of increasing the manufacturing cost. Further, the above circuit configuration has a disadvantage that high frequency noise is mixed in from the ground terminal side. That is, the ground terminal is actually connected to the power supply ground by a power supply line. This is because the power supply line has a non-negligible impedance for a high-frequency signal of several tens of MHz or more.

FIG. 8 shows an example of a practical use form of the stabilized power supply circuit 10. As shown in FIG. The stabilized power supply circuit 10 is connected to a power supply E and a load 30 by a power supply line 40 as shown in the figure. The impedance 20 between the ground terminal of the stabilized power supply circuit 10 and the power supply line 40 represents the impedance due to the wiring length between them.

The impedance 20 is a value that can be ignored for a low-frequency signal, but cannot be ignored for a high-frequency signal. In recent years, electronic devices such as mobile phones and computer devices emit high-frequency radio waves in the band of several tens of MHz to several GHz, which become noise and invade from any terminal of the circuit to cause malfunction. These high-frequency radio noises enter the input terminal, the output terminal, or the ground terminal and fluctuate the output voltage. The ground terminal
As described above, since there is a certain impedance between the power supply line and the ground, high-frequency noise enters. Malfunctions such as fluctuations in the DC output voltage due to such high-frequency radio noise have been particularly pointed out in recent years.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to remove a high-frequency noise from a feedback signal of an amplifier to output a constant voltage even when external noise exists. To provide a stabilized power supply circuit.

[0009]

According to a first aspect of the present invention, there is provided a stabilized power supply circuit comprising an amplifier having a feedback circuit and a transistor circuit, wherein a transistor current is controlled in accordance with an output of the amplifier. A stabilized power supply circuit for making the output voltage constant, characterized in that a feedback circuit of the amplifier is provided with a noise removing filter.

A stabilized power supply circuit according to a second aspect of the present invention is characterized in that, in addition to the feedback circuit of the amplifier, the output terminal of the stabilized power supply circuit is provided with a noise removal filter.

Further, the stabilized power supply circuit according to the present invention is characterized in that a capacitive element or an inductive element is used for the noise removing filter.

[0012]

According to the stabilized power supply circuit of the first aspect, the amplifier has a noise removing filter in its feedback circuit. This noise removal filter is, for example, a grounded capacitive element. Therefore, it has a low impedance with respect to high-frequency noise, and suppresses high-frequency noise from entering the input of the amplifier. As a result, even if there is high frequency noise, the output voltage is always kept constant without being reduced. The stabilized power supply circuit according to claim 1 includes a noise removal filter in a feedback circuit of the amplifier,
The above noise is removed. Therefore, the fluctuation of the DC output voltage can be eliminated.

Further, the stabilized power supply circuit of the present invention has a noise removal filter at the output terminal in addition to the input of the feedback circuit of the amplifier. The high frequency noise that has entered the stabilized power supply circuit also reaches the base of the output transistor connected to the output terminal of the amplifier. The emitter current of the output transistor fluctuates due to the high frequency noise entering the base, and the output of the stabilized power supply circuit fluctuates. According to the present invention, a noise elimination filter including a grounded capacitive element is provided between the output terminal of the amplifier and the output transistor. Thereby, the amplified high-frequency noise is bypassed to the ground side and reduced. Therefore, the output voltage of the stabilized power supply circuit is maintained.

Further, according to the stabilized power supply circuit of the third aspect, a capacitive element or an inductive element is used for the noise removing filter. The capacitive element is, for example, the above-described capacitor, and can be easily manufactured by existing semiconductor integration technology. Therefore, a small and inexpensive stabilized power supply circuit that does not require an external capacitor can be provided.

When miniaturization is not required, the noise elimination filter may be an inductive element. This inductive element is a magnetic element such as a coil or a ferrite that absorbs high-frequency noise. In this case, the one terminal is used without being grounded and inserted in series with the line of the feedback circuit. Alternatively, it is arranged in an inductive coupling with a target line. Inductive elements have low impedance for direct current and high impedance for high frequency noise.
Dance. As a result, high-frequency noise does not flow into the feedback circuit. Therefore, the output of the stabilized power supply circuit is not reduced for the same reason as described above.
When the inductive element is inserted into the output terminal of the amplifier, high-frequency noise is not transmitted to the next transistor because of high impedance. Therefore, high frequency noise is not mixed into the output for the same reason as described above, and a stable output voltage can be obtained.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following examples. FIG. 1 is a circuit diagram of a stabilized power supply circuit 10 according to the present invention. The main configuration of the circuit is the same as that of the conventional example. The feature of the present embodiment is that a capacitor C1 which is a capacitive element is connected to the feedback line 14 of the feedback circuit 13. Further, a capacitor C2 which is also a capacitive element is connected to the output terminal of the amplifier 11. The capacitances of the capacitors C1 and C2 are 50 pF, 1
0 pF, for example, a low impedance for a high frequency signal of 100 MHz or more. Further, as described above, since the impedance between the ground terminal and the ground has an impedance due to the length of the wiring, the impedance is represented by the impedance Z1.

FIG. 2 shows a stabilized power supply circuit 10 according to the present invention.
FIG. This is a 5V output stabilized power supply circuit. When 5 V or more, for example, 12 V is applied to the input terminal, 5 V is output. Although this circuit diagram includes an overvoltage protection circuit or a temperature compensation circuit, the basic configuration is the same as that of FIG. Note that the same parts are given the same numbers.

The basic operation of this circuit for constant voltage is the same as that of the conventional example. Here, the operation of the capacitors C1 and C2 will be mainly described with reference to FIG. As described above, for mobile phones and the like, several tens of MHz to several GH
An electromagnetic wave of z is emitted. Then, the electromagnetic wave enters from each terminal of the stabilized power supply circuit. In the figure,
The transistor q6 is connected to the inverting input terminal of the amplifier 11, and the transistors q7 and q8 are connected to the amplifier 1
One amplification stage is constituted. Of the high-frequency noise that has entered from each terminal, the component passing through the path of the input transistor q6, the resistor R6, and the transistors q7, q8 shown in the figure causes the base-emitter voltage V _{BE of} these transistors to be increased.
And the output voltage fluctuates. Its output voltage V
_OUT2 is given by the following equation.

V _OUT2 = (V _BE ) _q6 + (V _BE ) _q7 + (V _BE ) _q8 + I ₁ R1 + I ₂ R6 (3) where (V _BE ) _q6 , (V _BE ) _q7 , (V _BE ) _q8 are the base-emitter voltages of the transistors q6, q7, q8, respectively. Further, I ₁ is the emitter current of flowing through the resistor R1 transistor q5 (transistor 12), I ₂ is the current flowing through resistor R6 in the interior of the amplifier. Therefore, the base-emitter voltage V of these transistors
_{If BE} changes due to high frequency noise, output voltage V _OUT2 changes. The high frequency noise propagated to the bases of the transistors q6, q7, q8 is
The emitter-to-emitter voltage V _BE is changed sinusoidally. Therefore, rectification of these high-frequency noises occurs in the junction diode formed between the base and the emitter. This rectification, V _BE -I _B characteristic of the transistor varies effectively. That, V _BE voltage for supplying the same I _B is to effectively decrease the high frequency noise. This is,
This is a malfunction mechanism of the stabilized power supply circuit due to high frequency noise. Capacitor C1 reduces high frequency noise applied to the bases of these transistors. Thereby, the fluctuation of the output voltage is suppressed.

Further, part of the high-frequency noise that has entered the circuit reaches the base of the output transistor 12, and the rectification at the base-emitter junction effectively changes the emitter current of this transistor. This emitter current is I ₁ in equation (3). Therefore, the output voltage fluctuates from the equation (3). The capacitor C2 reduces high-frequency noise applied to the bases of these transistors and suppresses fluctuations in output voltage.

FIG. 3 shows a comparison of characteristics when capacitors C1 and C2 are provided and when they are not provided. This is a DC voltage characteristic of the output terminal when a high frequency signal of, for example, 100 MHz is superimposed in a state where, for example, 12 V is applied to the input terminal in order to compare the performance. Terminals on which the high-frequency signal is superimposed are an input terminal, an output terminal, and a ground terminal. Here, the high frequency signal corresponds to actual high frequency radio noise. Therefore, the high-frequency signal, the high-frequency noise, and the RF in the figure are used interchangeably. In FIG. 3, the horizontal axis represents the power of the high-frequency signal, and the vertical axis represents the DC output voltage.

FIG. 3A shows the result of output characteristics when a high-frequency signal is superimposed on the input terminal, FIG. 3B shows the result of superimposition on the output terminal, and FIG. 3B shows the result of superimposition on the ground terminal. It is shown in FIG. The solid line shows the result of the present embodiment in which a countermeasure is taken, and the dotted line shows that of the conventional example without the countermeasure. In any case, when the capacitors C1 and C2 are provided,
The output voltage is kept almost constant. Capacitors C1, C2 are connected to the feedback circuit 13 and the output terminal of the amplifier 11, respectively.
It can be seen that the present invention having the above has a remarkable effect on electromagnetic noise.

In the conventional case without the capacitors C1 and C2, the high-frequency noise penetrating from each terminal is reduced by the output transistor 12, the input transistor q6 of the amplifier,
And the signal propagates to the transistors q7 and q8 in the amplification stage.
The propagated high-frequency noise is rectified between the base and the emitter of these transistors, and changes the DC characteristics of the transistors. As a result, the output voltage decreases as shown in FIGS.

As can be seen from the above description, if the feedback circuit of the stabilized power supply circuit and the noise elimination filter including the capacitor are provided at the output terminals of the amplifier, the stabilized power supply circuit is not affected by high frequency noise such as electromagnetic wave noise. it can.

In the above example, the capacitor C1 is provided on the feedback line 14 and the capacitor C2 is provided on the output terminal of the amplifier. However, if a sufficient effect can be obtained by using only the capacitor C1, as shown in FIG. It is not necessary to use it. When the capacitors C1 and C2 are formed on a silicon substrate, they may be formed of an insulating film and a conductive film as shown in FIGS. 5A and 5B, or the collector and the emitter of the transistor may be grounded. It may be constituted by making it.

(Modifications) Although one embodiment of the present invention has been described above, various other modifications are possible. FIG.
(A) shows a modification of the stabilized power supply circuit of the present invention. The difference from the above-described embodiment is that an inductive element is provided instead of the above-mentioned capacitive elements such as the capacitors C1 and C2. The inductive element is, for example, a coil having high impedance with respect to a high-frequency signal, and is a magnetic element such as ferrite that absorbs high-frequency noise. The circuit configuration and the circuit operation are the same as those in the above embodiment.

In the above embodiment, the feedback line 14
And the output terminals of the amplifier were provided with capacitors C1 and C2, respectively, so that high-frequency noise was bypassed to the ground terminal side. Alternatively, the above-described inductive element or a magnetic element such as ferrite may be used to block or absorb high frequency noise. In short, it is sufficient to remove high-frequency noise from the feedback line 14.

For example, if the feedback line 14 is provided with a ferrite Z2, which is a magnetic element, it is possible to absorb only high frequency noise without affecting DC. Further, a coil L1 may be used instead of the capacitor C2 at the output end of the amplifier. If the coil L1 having high impedance against high frequency noise is provided, high frequency noise is blocked and does not flow into the base of the transistor 12. Therefore, the output voltage is not affected. Even with such a configuration, a similar stabilized power supply circuit can be realized.

In the above modification, a magnetic element is provided on the feedback line and an inductive element is provided on the output end of the amplifier. However, in the case where a sufficient effect can be obtained by using only the magnetic element, it is shown in FIG. Thus, the inductive element L1 may not be used. Such a circuit configuration may be used.

Further, in the above embodiment or the modified example, the noise removing filters having the same property are used, but they may be mixed. For example, a capacitive element may be used for the feedback line 14 and an inductive element may be provided at the output terminal of the amplifier. Further, the inductive element may be inserted directly into the circuit or may be inserted in series into the circuit by magnetic coupling. Further, a coil having ferrite as a core may be used as the inductive element.

[Brief description of the drawings]

FIG. 1 is a stabilized power supply circuit diagram according to an embodiment of the present invention.

FIG. 2 is a detailed circuit diagram of the stabilized power supply circuit according to the embodiment of the present invention.

FIG. 3 is a comparison characteristic diagram of an output voltage between the present embodiment and a conventional example.

FIG. 4 is a modified circuit diagram of the stabilized power supply circuit according to the embodiment of the present invention.

FIG. 5 is a diagram showing a capacitor according to an embodiment of the present invention and a modification thereof.

FIG. 6 is a stabilized power supply circuit diagram using an inductive element and a magnetic element according to a modification of the present invention.

FIG. 7 is a diagram of a conventional stabilized power supply circuit.

FIG. 8 is a block circuit diagram of a stabilized power supply circuit affected by high-frequency noise according to a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Stabilized power supply circuit 11 Amplifier 12 Transistor 13 Feedback circuit 14 Feedback line 15 Reference voltage generation circuit C1, C2 Capacitor L1 Coil R1 Monitor resistance R2 Monitor resistance Z1 Impedance by wiring between ground terminal and ground Z2 ferrite

Continued on the front page F term (reference) 5G065 AA00 EA01 HA04 JA01 LA01 MA03 NA01 NA03 NA04 5H430 BB01 BB05 BB09 BB11 EE02 EE12 FF02 FF13 GG08 HH03

Claims (3)

[Claims] 1. A stabilized power supply circuit comprising an amplifier having a feedback circuit and a transistor circuit, wherein the stabilized power supply circuit controls the current of the transistor in accordance with the output of the amplifier and keeps the output voltage constant. And a noise removing filter. 2. The stabilized power supply circuit according to claim 1, wherein the amplifier includes a noise removing filter at an output terminal. 3. The stabilized power supply circuit according to claim 1, wherein the noise removal filter is formed of a capacitive element or an inductive element.